The phrase you mentioned in Russian sounds as 'Beware of Danayans bearing gifts'. Its ethimology has something to do with the legend of 'Troyan Horse'. The impregnable city of Troya was invaded by sly Danayans who presented a huge wooden statue of a horse to the city as a sign of reconcilliation. The Troyans accepted the gift and at night Danayan (Greek?) soldiers hidden inside the horse came out and opened the city gates for their troops waiting outside.

'Beware of Danayans bearing gifts' means 'Don't trust your enemies trying to please you'. I don't know if 'Greeks' is the proper word in the English variant of this phrase.